a review of carbon disulfide exposure data and the association between carbon disulfide exposure and...

REGULATORY TOXICOLOGY AND PHARMACOLOGY 26, 119–128 (1997)ARTICLE NO. RT971107

A Review of Carbon Disulfide Exposure Data and the Associationbetween Carbon Disulfide Exposure and

Ischemic Heart Disease Mortality

Bertram Price,* Tamara S. Bergman,* Maribelle Rodrı́guez,* Richard T. Henrich,† and Elizabeth J. Moran‡

*Price Associates, Inc., Washington DC 20006; †Akzo Nobel Chemicals, Inc., Dobbs Ferry, New York 10522;and ‡Chemical Manufacturers Association, Arlington, Virginia 22209

Received March 11, 1997

has listed CS2 as a priority chemical for its currentprogram to revise permissible exposure limits (PELs)Recent regulatory efforts have devoted attention to(OSHA, 1996).carbon disulfide (CS2) exposure and its potential ef-

fects on the cardiovascular system. To investigate the EPA’s establishment of the RfC considered reproduc-association between CS2 exposure and ischemic heart tive, developmental, neurotoxic, and cardiovasculardisease (IHD) mortality, the analysis presented here endpoints. To derive the numerical value for the RfC,had the following objectives: (i) to review historical EPA focused on peripheral nervous system (PNS) end-CS2 exposure data in the viscose rayon industry and points and applied the benchmark concentration meth-identify trends and (ii) to use these historical data to odology (IRIS, 1995; Price and Berner, 1995; Setzer,suggest a standard mortality ratio (SMR)–exposure re- 1995). Subsequently, Price et al. (1996) conducted anlationship and a threshold level for occupational expo- analysis that confirmed the BMC for PNS endpointssure to CS2. CS2 exposure data were extracted from

and demonstrated that cardiovascular risk factors didpublished studies and used with the SMR versus expo-not increase for exposure concentrations below 15 ppm.sure score relationship developed by Sweetnam et al.

The scientific literature on CS2 includes studies of(Br. J. Ind. Med. 44, 220–227, 1987) to relate SMRs di-IHD mortality for workers in the viscose rayon industryrectly to exposure. Upper and lower bound exposure(Liss and Finkelstein, 1996; MacMahon and Monson,profiles were derived and used to identify exposure1988; Nurminen and Hernberg, 1985; Swaen et al.,thresholds. For an IHD SMR equal to 100, the upper

and lower bound exposures were 60 and 20 ppm, re- 1993; Sweetnam et al., 1987; Tiller et al., 1968; Tolonenspectively. The analysis indicates that the risk of IHD et al., 1979). Some of these studies show elevated stan-mortality and its relationship to CS2 exposure is mean- dard mortality ratios (SMRs) for workers occupation-ingful only for workers exposed to high levels for many ally exposed to CS2. The interpretation of these studiesyears. These high levels, which existed many years for regulatory application is limited because exposureago, are no longer found in the workplace. The results data based on personal monitoring are sparse. The lackof this analysis suggest a safe regulatory exposure of data, therefore, prevents the direct identification oflevel for CS2 between 15 and 20 ppm. q 1997 Academic Press a threshold exposure level or PEL. Some authors de-

rived an SMR–exposure relationship based on expo-sure categories or an exposure score (MacMahon andINTRODUCTIONMonson, 1988; Sweetnam et al., 1987). Although theseapproaches establish an association between IHD mor-Exposure to carbon disulfide (CS2) has been associ-tality and CS2 exposure, they do not contain sufficientated with increased risk of cardiovascular disease, isch-information to establish a threshold exposure level foremic heart disease (IHD) mortality, and adverse effectsregulatory purposes (e.g., a PEL).on the nervous and reproductive systems (Davidson

The research reported here consisted of an effort toand Feinleib, 1972; Fajen et al., 1981). Recently, regu-fill the historical CS2 exposure data gap and to inter-latory interest in CS2 has been expressed by the Envi-pret those data in terms of IHD mortality risk. Specifi-ronmental Protection Agency (EPA) and the Occupa-cally, the research had two objectives: (i) to review andtional Safety and Health Administration (OSHA).summarize historical exposure data reported in the sci-Based on reviews and analyses of literature on CS2

entific literature and identify exposure trends and (ii)exposure and its health effects, EPA established a ref-erence concentration (RfC) for CS2 (IRIS, 1995). OSHA to use these historical data to suggest a SMR–exposure

119 0273-2300/97 $25.00Copyright q 1997 by Academic Press

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120 PRICE ET AL.

TABLE 1Observed and Expected Deaths and SMRs by Exposure Score among Operatives: Ages 45 to 64,

Period of Follow-up 1950–82

IHD Other circulatory All causesExposure

score Obs Exp SMR Obs Exp SMR Obs Exp SMR

0–99 4 8.1 49 6 4 150 20 26.2 76100–199 25 26.3 95 21 12.4 169 87 82.9 105200–299 47 25.4 185 9 11.9 76 106 79.9 133§300 47 21.4 220 18 10.8 167 98 70.6 139

Note. Tests for trend: all causes x2 (1 df) Å 8.1, P õ 0.01; IHD x2 (1 df) Å 18.4, P õ 0.001. Reproduction of Table 5 from Sweetnam etal. (1987) Br. J. Ind. Med. 44, 220–227.

relationship and a threshold level for occupational ex- drogen sulfide (H2S) exposures. The current analysisonly addresses exposure to CS2; therefore, studies thatposure to CS2.did not distinguish CS2 from H2S exposures were ex-cluded.DATA

CS2 exposure data were reported in the studies inseveral different formats: one measurement or oneIn this analysis, two types of data were used: (i) CS2

sample taken at one point in time; an average of severalair concentrations and (ii) exposure scores (Table 1,samples over 1 year; averages of several samples overreproduction of Table 5 of Sweetnam et al., 1987). Theseveral years; and a range of averages over severalCS2 air concentrations were compiled from a literatureyears. Data reported as time-weighted averages werereview and consist of measurements collected at vari-not included in the analysis.ous rayon facilities between the years 1940 and 1995.

Often, exposure data were reported based on jobAll CS2 air concentrations were interpreted as ex-title or activity along the manufacturing line. The ma-posure levels and used to characterize the historicaljor job activities with potential for exposure to CS2 intrend of CS2 workplace exposure. The exposure scoresthe viscose rayon industry are viscose preparation,(Sweetnam et al., 1987), which reflect intensity andchurning, spinning, cutting, washing, and bleaching.duration of exposure, were coupled with the CS2 air

Exposure data were reported as either personal orconcentrations to establish an IHD SMR–exposure re-area samples. Personal monitoring data were availablelationship.after 1979. Area monitoring data were available for theyears 1941 to 1995.CS2 Air Concentrations

CS2 air concentrations (subsequently referred to asexposure data) were extracted from 15 published stud- Exposure Scoresies conducted in 11 countries, including the UnitedStates (Balcarova and Halik, 1991; Chu et al., 1995; Table 1 shows a relationship between IHD SMR and

an exposure score derived by Sweetnam for 1664 work-Cicolella and Vincent, 1984; Cirla and Graziano, 1981;Drexler et al., 1994; Fajen et al., 1981; Kamal et al., ers in the 1950–1982 follow-up period. Subsequently,

we used these data to translate the SMR–exposure1991; Liss and Finkelstein, 1996; Nurminem andHernberg, 1985; Paluch, 1948; Sugimoto et al., 1984; score relationship to an SMR–exposure relationship.

Sweetnam’s exposure scores were based on an indexSwaen et al., 1993; Vanhoorne et al., 1991; Vigliani,1954; Zhou et al., 1988). The studies contained CS2 associated with job type and exposure intensity. The

index ranges from 0 to 4. Nonviscose process operativesexposure data for a total of approximately 16,000 work-ers occupationally exposed in viscose rayon factories. with no exposure were assigned a rating of 0; nonvis-

cose process operatives with little exposure were as-These data were used to characterize the historicaltrend of CS2 exposure in the viscose rayon industry. signed a rating of 1; viscose process workers and other

jobs with intermittent exposures were assigned a rat-The initial literature search produced approximately30 studies that mentioned CS2 exposure or the viscose ing of 2 (moderate exposure); washers working within

the spinning department were assigned a rating of 3rayon industry (ENVIRON, 1996; Henrich, 1996). Sev-eral studies had to be excluded because they contained (high exposure); and spinners were assigned a rating

of 4 (highest exposures). The exposure score for eachdata that were not specific to the viscose rayon indus-try; reported exposure categories (high, medium, and individual is defined as a weighted sum of the index

values where the weights are the numbers of monthslow), not exposure numbers; or combined CS2 and hy-


121CARBON DISULFIDE EXPOSURE AND ISCHEMIC HEART DISEASE MORTALITY

spent in each job type. The exposure score may be ex-AES Å ∑

4

iÅ0

irti

120Å ∑

4

iÅ 0

irpi , (2)pressed as

where {pi} are the proportions of time a worker wouldES Å ∑

4

iÅ0

irti , (1) have spent in a particular job type. The objective wasto obtain an average exposure level (AE), expressed asa concentration (ppm), for each exposure score range.

where {i } are the exposure indices and {ti} are the The average exposure level is expressed asmonths spent in a particular job type. Sweetnam re-ports the exposure scores as ranges: 0–99, 100–199,

AE Å ∑4

iÅ0

Xirpi , (3)200–299, and greater than or equal to 300 (seeTable 1).

where {Xi} are CS2 concentrations in ppm associatedwith each job category. The {Xi} are determined fromMETHODSthe exposure data compiled from the CS2 literature.The {pi}, however, are unknown.Trend in CS2 Occupational Exposure

Two sets of {pi} were derived: a set corresponding toan upper bound exposure and a set corresponding to aTo explore trends in exposure, the CS2 exposure datalower bound exposure. The upper bound and lowerwere organized using the following rules: (i) one mea-bound exposures were obtained by finding the {pi} thatsurement or sample taken at one point in time wasmaximize and minimize AE, subject to specific con-reported to be representative of the exposure for thatstraints. The two solutions were obtained by linear pro-entire year; (ii) annual averages were reported as theygramming (Hillier and Lieberman, 1990). Formally,appear for the year given in the study; (iii) where onethe linear programming problem can be stated asaverage exposure number was given for a range of

years, the last year of the range was used in the analy-sis; and (iv) where a range of exposure values for an Maximize AE Å ∑

4

iÅ0

Xirpi (4)interval of several years was given, the average overthat exposure range was assigned to the last year ofthe time interval. or

All data, without regard to job category, were plottedversus year of exposure to characterize the overall

Minimize AE Å ∑4

iÅ0

Xirpi (5)trend of occupational exposure to CS2. These data arepresented in Fig. 1.

The data then were assigned to one of four job catego-subject tories: Churning, Spinning, Washing, and Other. Data

reported in the studies for viscose preparation or0 £ pi £ 1, (6)churning activities were classified as Churning. Data

reported for spinning or cutting activities were classi-∑4

iÅ0

pi Å 1, (7)fied as Spinning. Data collected for washing or bleach-ing activities were classified as Washing. If data didnot correspond to any of the above categories, they were

andlisted as Other. The Other category was included inthe analysis of all data. Data for the Churning, Spin-ning, and Washing categories are presented in Figs. 2, ∑

4

iÅ0

irpi Å AES. (8)3, and 4.

The {Xi} were assigned values that reflect exposuresIHD SMR versus Exposure Relationshipduring the years 1940 to 1960, the principal time ofexposure for Sweetnam’s cohort. The {Xi} for each jobWe translated Sweetnam’s exposure scores to expo-

sure levels in ppm units as follows. The midpoint of category are averages of CS2 concentration data for theyear 1946, the most complete data set closest to theeach exposure score range in Table 1 was selected to

represent the range. For the greater than or equal to midpoint of the time interval. CS2 concentrations wereassigned as follows: X0 Å 0 represents no exposure;300 range, 400 was used. Then, assuming a 10-year

exposure period for all workers, an average exposure X1 Å 16.5 ppm, the midpoint between X0 and X2 , wasassigned to low exposures; X2 Å 33 ppm, the averagescore (AES) was calculated for each interval by dividing

by 120 months: concentration for Churning, was assigned to moderate


122 PRICE ET AL.

FIG. 1. Carbon disulfide exposure versus year, all data.

exposures; and X3 Å X4 Å 155 ppm, the average expo- graph of Churning exposures, the CS2 exposure aver-sure concentration of Spinning and Washing, was as- age is 51 ppm in the 1940s and declines to less thansigned to both high and highest exposures. This desig- 10 ppm in the 1990s. For Spinning, Fig. 3 shows annation is consistent with Sweetnam’s job type rating. average of 155 ppm in the 1940 time frame and again

a decrease to around 14 ppm in the 1990s. Figure 4RESULTS demonstrates the same trend of decline for Washing

from 285 ppm in the 1940s down to 11 ppm in 1990s.Trend in CS2 Occupational Exposure In Figs. 1 and 3, data reported in the Chu et al. (1995)

study and one point from the Liss (1996) study deviateThe CS2 exposure data versus year are presented insignificantly from other data reported from 1979 to theFigs. 1–4. A downward trend of CS2 exposure over thepresent. The points, which correspond to CS2 concentra-time interval of 1940 to 1995 is demonstrated in thetions of hundreds of ppm, appear to be data anomalies.plot of all data (Fig. 1) and in the plots for each jobAlthough these points are presented in Figs. 1 and 3, theycategory (Figs. 2, 3, and 4).were not included in any subsequent numerical calcula-Figure 1, which contains all data, shows a decline intions. (Inclusion of these three points would produce aCS2 exposure from an average of 158 ppm in the 1940s

to approximately 14 ppm in the 1990s. In Fig. 2, the slightly elevated average for CS2 exposure in the 1990s.)

FIG. 2. Carbon disulfide exposure versus year, churning data.



FIG. 3. Carbon disulfide exposure versus year, spinning data.

IHD SMR versus Exposure Relationship proximately 60 ppm. For the curve representing thelower bound exposure profile, the point of intersectionTwo exposure profiles corresponding to Sweetnam’s is 20 ppm.exposure scores were developed for the 1940 to 1960

time interval: one reflecting upper bound exposure lev-DISCUSSIONels and the other reflecting lower bound exposures lev-

els. Table 2 presents the upper bound and lower boundaverage exposure values obtained for each of the four In the production of viscose rayon, several process

steps are common to manufacturing facilities world-exposure score ranges.Figure 5 displays the relationship between the IHD wide (Stewart, 1996). These steps include viscose prep-

aration, churning, spinning, and washing. Therefore,SMR and exposure concentrations for the two expo-sure profiles. The horizontal dashed line drawn across exposure data from studies conducted at facilities in

countries other than the United States are useful forFig. 5 corresponds to an SMR equal to 100. The CS2

concentrations where the SMR equal to 100 intersects characterizing the historical trend in worker exposureto CS2.the curves may be interpreted as exposure thresholds

or safe levels. For the curve representing the upper Based on the CS2 exposure data extracted from pub-lished studies, there is a downward trend in CS2 expo-bound exposure profile, the point of intersection is ap-

FIG. 4. Carbon disulfide exposure versus year, washing data.


124 PRICE ET AL.

TABLE 2Upper Bound and Lower Bound Average Exposures

Exposurescore

interval ES AES Max/min p0 p1 p2 p3 p4 AE

0–99 50 0.42 Min 0.79 0.00 0.21 0.00 0.00 6.93Max 0.86 0.00 0.00 0.14 0.00 21.70

100–199 150 1.225 Min 0.37 0.00 0.63 0.00 0.00 20.60Max 0.58 0.00 0.00 0.42 0.00 64.60

200–299 250 2.08 Min 0.00 0.00 0.96 0.00 0.04 37.90Max 0.31 0.00 0.00 0.69 0.00 108.00

§300 400 3.33 Min 0.00 0.00 0.33 0.00 0.67 114.00Max 0.00 0.00 0.00 0.67 0.33 155.00

Note. ES, midpoint of Sweetnam’s exposure score range; AES, average exposure score; pi , proportion of time worker spends in job typei; AE, average exposure.

sure over time in the viscose rayon industry. CS2 air information to evaluate the trend of CS2 exposure overthe 1940 to 1995 time frame. The trend analysis, there-concentrations were high in the 1940s (158 ppm) and

have declined through the years (14 ppm). Downward fore, includes area monitoring data. Personal and areamonitoring data are expected to reflect the same pat-trends also are shown when the data are classified by

process as demonstrated in Figs. 2, 3, and 4. While terns over time.Although shown in Figs. 1 and 3, three exposurespinning is believed to be the source of the highest

exposures (Sweetnam et al., 1987), exposure data mea- measurements were excluded in the calculation of aver-ages used to demonstrate the trend. The first data pointsured in the 1940s in the analysis were higher for

Washing than for Spinning. This apparent discrepancy corresponds to a 10-min intermittent exposure concen-tration of 254.4 ppm (Liss and Finkelstein, 1996). Thisis due to the fact that during the years 1940 to 1946

spinning and washing activities occurred in the same measurement is not representative of average daily ex-posure to CS2 in the viscose rayon industry. The otherroom and it was difficult to separate exposure reliably

due to these job categories (Paluch, 1948). two data points correspond to average concentrationsof 58 and 225 ppm measured in a Chinese viscose rayonAlthough personal monitoring is preferable for as-

sessing exposure, personal air samples were available plant (Chu et al., 1995). These concentrations, however,are not representative of current average CS2 concen-only after 1979. The personal monitoring data reflect

the uniformly low exposure levels currently found in trations in the United States and Europe. Inclusion ofthese three points would produce a slightly elevatedthe industry, but they alone do not provide sufficient

FIG. 5. IHD SMR versus carbon disulfide exposure, exposure years 1940–1960. IHD, ischemic heart disease; SMR, standard mortalityratio.



TABLE 3Observed and Expected Deaths and SMRs by Exposure Score among Operatives: All Ages,

Period of Follow-up 1950–1982

IHD Other circulatory All causesExposure

score Obs Exp SMR Obs Exp SMR Obs Exp SMR

0–99 28 28.1 100 28 20 140 94 95.5 98100–199 79 68.1 116 68 42.5 160 261 223 117200–299 80 58.1 138 48 34.4 140 236 188.4 125§300 80 55.7 144 57 35.8 159 227 186.7 122

Note. Tests for trend: all causes x2 (1 df) Å 2.7, NS; IHD x2 (1 df) Å 4.0, P õ 0.05. Reproduction of Table 6 from Sweetnam et al. (1987).Br. J. Ind. Med. 44, 220–227.

average for exposures in the 1990s but would have no addition, exposure data for nonviscose process opera-tives were not explicitly identified in the studies usedeffect on the SMR–exposure relationship shown in Fig.

5, which was derived from the 1940 to 1960 data. for the trend analysis. Sweetnam includes these work-ers in his analysis and it was necessary to provide anIn the trend analysis plots, no data are presented for

the years 1947 to 1964. This occurs for one of two rea- exposure value representing X1 , the low exposure cate-gory. X1 was set equal to 16.5 ppm, the midpoint be-sons: either there are no data available for those years

or the data were reported over a range of years that tween X0 (0 ppm) and X2 (33 ppm). Since p1 Å 0 in theequation for AE (Table 2), X1 could be smaller or largerencompassed the time frame 1947 to 1964 and they

were assigned to the last year of that range. This as- without affecting our SMR–exposure relationship orour determination of an exposure threshold. Further-signment was necessary in order to have a consistent

method for handling complex data. Although no mea- more, the linear programming solution for p1 will al-ways be zero as a consequence of the numerical valuessurements are shown for this time interval, it is likely

that CS2 exposure levels declined during this period to associated with Sweetnam’s exposure score ranges.Based on the association between IHD mortality andreach the low levels recorded after 1965.

The exposure data shown in Figs. 1–4, although CS2 exposure between 1940 and 1960, a thresholdvalue of 20 ppm was obtained (Fig. 5). A sensitivitysparse for some years, provide an adequate character-

ization of the downward historical trend of worker ex- calculation was conducted to determine the effect onthe results if CS2 concentrations from the trend analy-posure. This downward trend is consistent with state-

ments made in other studies that worker exposure to sis were overstated and actual concentrations werelower than reported. (It is not necessary to consider ifCS2 has declined over time (Swaen et al., 1993; Hern-

berg et al., 1970; Tolonen et al., 1979; Cirla and Grazi- CS2 levels were higher than reported for this wouldlead to a higher and therefore less conservative thresh-ano, 1981; MacMahon and Monson, 1988).

Data from the trend analysis were used to investi- old value.) A reduction of all {Xi} by 20% translatesdirectly to a 20% reduction in the threshold level togate exposure levels that may be interpreted as a

threshold or safe exposure level for CS2 using the IHD around 16 ppm, which is not substantively differentfrom the original solution of 20 ppm.SMR–exposure relationship. The trend data were

needed to estimate worker exposures between 1940 and The SMRs for Sweetnam’s cohort were constructedby comparing the number of expected deaths in the1960, the principal time of exposure for Sweetnam’s

cohort. The 1946 data provide the most complete data reference population with the number of deaths ob-served in the exposed cohort, adjusted for age and sex.set closest to the midpoint of the 1940 to 1960 time

interval. Other factors that may affect mortality due to IHDinclude race, body mass index, smoking status, diet,CS2 concentrations from the trend analysis were

used as an estimate of exposure for Sweetnam’s cohort and educational level (Egeland, 1992; Price et al.,1996). These confounding factors have the ability toand were assigned to the {Xi} of Eqs. (4) and (5), based

on Sweetnam’s job type rating. When assigning concen- alter the association between the IHD–SMR and CS2

exposure. For example, if smoking, a major risk factortrations to X3 and X4 (high and highest exposure), itwas difficult to separate exposure due to spinning and for heart disease, were more prevalent in Sweetnam’s

cohort than in the reference population, the number ofwashing reliably. This is due to the fact that duringthe years 1940 to 1946 spinning and washing activities deaths in Sweetnam’s cohort attributable to CS2 expo-

sure and the SMR would be overstated. As a conse-occurred in the same room (Paluch, 1948). Therefore,the data for the two categories were combined and the quence, the SMR–exposure curve in Fig. 5 would be

shifted down, resulting in a threshold value greateraverage (155 ppm) was assigned to both X3 and X4 . In


126 PRICE ET AL.

than 20 ppm. If smoking in Sweetnam’s cohort wereless prevalent than in the reference population, thereverse would be true. The result then would be athreshold value lower than 20 ppm. There are, how-ever, no data to suggest that smoking habits or thedistribution of any other confounding factor for subjectsin Sweetnam’s cohort differs from those in the refer-ence population in a manner that would cause the de-rived threshold value of 20 ppm to be overstated.

An SMR equal to 100 was employed to identify thethreshold or safe exposure level. An SMR equal to 100means no excess deaths occur in the cohort relative tothe reference population. It could be argued that inoccupational studies, the healthy worker effect dictatesusing an SMR lower than 100 as a threshold (McMi-chael, 1976). The healthy worker effect is a selectionbias arising in occupational groups because of goodhealth status related to initial and continued employ-ment. According to Sweetnam, the healthy worker ef-fect has no role in the interpretation of his data becauseall members of his cohort have been working for at least10 years before they enter the period of observation inhis study. Sweetnam argues that 10 years is a sufficienttime for the healthy worker bias to dissipate. Addi-tional support for the absence of the healthy workereffect is contained in SMR results reported for the leastexposed workers (i.e., exposure score between 0 and99) in Tables 1 and 3 of this report. The SMRs formortality due to all causes and mortality due to IHDare not statistically different from 100 (statistical testsnot included). If this group of workers approximates acontrol group (i.e., no CS2 exposure), then the SMRsequal to 100 indicate the absence of a healthy workereffect. Empirical evidence that there is no healthyworker effect in Sweetnam’s study would be strongerif an SMR statistically equal to 100 had been calculatedfor a control group of unexposed workers (i.e., CS2 con-centration equal to 0 ppm). Sweetnam, however, re-ports no such calculation.

The study conducted by MacMahon and Monson(1988) (subsequently MacMahon), which includes alarger number of rayon workers than any previousstudy, also relates IHD mortality to CS2 exposure. Mac-Mahon uses exposure categories but does not translatethese categories into numerical exposure data. There-fore, the IHD SMR–exposure relationship derived fromSweetnam’s data cannot be applied. However, MacMa-hon’s results indicate that only workers with heavy andprolonged exposure to CS2 are at risk of death due toIHD. Within this group of heavily exposed workers,statistically significant SMRs were found only forgroups first exposed in the 1940s and exposed for morethan 15 years (Table 4).

MacMahon’s results also suggest the absence of thehealthy worker effect. The SMR for death from allcauses in the No Exposure group is statistically equal

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TABLE 5Observed and Expected Numbers of Deaths and Standardized Mortality Ratios (SMR)

by Level of Exposure to Carbon Disulfide

Most exposed Least exposed No exposure(N Å 4448) (N Å 2230) (N Å 3311)

ICD 8Code Cause of death Obs SMR Obs SMR Obs SMR

— All causes 613 105 429 81* 338 108390–458 All circulatory disease 311 114** 238 88** 163 119**410–414 Arteriosclerotic heart disease 242 124* 164 85** 108 108

Note. Reproduction of Table 3 from MacMahon and Monson (1988). J. Occup. Med. 30 (9), 701–702 (relevant causes of death only).* Differs from 100 with P õ 0.01.

** Differs from 100 with P õ 0.05.

is statistically equal to 100 (Table 5). Although biases REFERENCESin the data discussed by MacMahon could be responsi-

Balcarova, O., and Halik, J. (1991). Ten year epidemiological studyble for the overstated SMRs in the No Exposure groupof ischaemic heart disease in workers exposed to carbon disulphide.(e.g., low socioeconomic status and high stress level ofSci. Total Environ. 101, 97–99.the work), MacMahon asserts that at least for workers

Chu et al. (1995). Polyneuropathy induced by carbon disulphide inwith 15 or more years of employment no residual of the viscose rayon workers. Occup. Environ. Med. 52, 404–410.healthy worker effect would be expected. Cicolella, A., and Vincent, R. (1984). Workplace pollution in viscose

MacMahon’s data indirectly support a threshold plants. G. Ital. Med. Lav. 6, 101–106.level for CS2 of 20 ppm corresponding to an SMR equal Cirla, A., and Graziano, C. (1981). Health impairment in viscose-to 100 by emphasizing the significance of exposures in rayon workers with carbon disulfide risk below 30 mg/m3. G. Ital.

Med. Lav. 3, 69–73.the 1940s and the absence of the healthy worker effect.Davidson, M., and Feinleib, M. (1972). Carbon disulfide poisoning:Results from Price et al. (1996), a study of PNS effects

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sure to carbon disulphide of workers in the viscose industry. Int.support for a threshold between 15 and 20 ppm or Arch. Occup. Environ. Health 65, 359–365.higher by showing no increase in cardiovascular risk Egeland et al. (1992). Effects of exposure to carbon disulphide on lowfactors for exposure levels up to 15 ppm. The NIOSH density lipoprotein cholesterol concentration and diastolic blooddatabase provides the most reliable data representing pressure. Br. J. Ind. Med. 49, 287–293.current occupational exposures in viscose rayon manu- ENVIRON (1996). Draft Report: Summary of Exposure Data and

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